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Arbabi, Nasser

University of British Columbia

An important step in the processing of unidirectional pre-impregnated composite laminates is debulking and compacting the layers to remove gaps between and within the laminae. During this step, the resin is heated up and can flow relative to the fibre bed. Consequently, the fibre bed’s elastic properties play a significant role in determining the pressure withstood by the fibre bed versus the resin, as well as in determining the resulting shear deformation of the prepreg. The flow of resin through the fibre bed is typically modeled by Darcy’s Law, and the fibre bed properties of interest are defined based on the fibre bed compaction curve, a stiffening curve relating the fibre bed's normal stress to its normal strain or volume fraction. The prevalent fibre bed model in literature is a simple analytical formulation that predicts the transverse modulus E_33, but it ignores the fibre bed's shear modulus. This thesis presents three main parts: First, a modified representative volume element is introduced, allowing for simultaneous prediction of the full elastic matrix with correlated transverse and shear moduli, both matching experimental measurements. This model represents all elastic properties through a single, coherent mechanical approach. Second, a statistical representation of the fibre bed is presented, incorporating inherent variations in fibres using the extended fibre bed model. This model establishes a direct connection between the material's mechanical response and the fibre bed architecture, including volume fraction and fibre waviness distribution. Results show that the shear modulus is more susceptible to variation due to non-homogenous fibre interactions creating nonuniform deformation during compaction. Third, classical micromechanical models' inadequacy in simulating prepreg behavior during initial resin curing stages is addressed. The extended fibre bed model is implemented, incorporating resin properties and enabling the calculation of the full elastic matrix for the prepreg as a unified system evolving based on compaction level and resin mechanical properties during curing. Coupling the prepreg micromechanical model with macro-level models provides a multiscale simulation framework necessary for accurate prediction of prepreg behavior throughout processing stages, from pre-gelation to solidified resin.

Text

2024-04-04

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87680

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/